Abrasive articles have long been known in the art, and have been used to abrade, finish, and polish a variety of surfaces. In its most basic form, a coated abrasive article comprises abrasive grains adhered to a backing. Paper and cloth have long been used as backing materials for coated abrasive articles. The abrasive grains may also be adhered to other types of backings, including inflexible backings.
Coarse-grade abrasive articles are used for rough sanding or abrading of a workpiece. At the other end of the spectrum, extremely fine abrasive grains, sometimes called microabrasive grains, are incorporated into coated abrasive articles and used to achieve a close tolerance finish or polish. Coated abrasive articles containing microabrasive grains are used, for example, for magnetic head finishing; polishing or burnishing floppy disks; creating high gloss finishes on an acrylic surface; and providing a final finish to stainless steel or brass.
Whether using microabrasive grains, coarse-grade abrasive grains, or other types of abrasive grains, the abrading surface of a coated abrasive article can be clogged or gummed by materials worn from the workpiece. One way this problem has been addressed is by applying the abrasive grains to the surface of a backing in a dot pattern or matrix. See, for example, U.S. Pat. Nos. 3,246,430 (Hurst); 794,495 (Gorton); 1,657,784 (Bergstrom); 4,317,660 (Kramis et al.). When abrasive grains are disposed in a pattern, pathways exist for abraded material to be removed.
Coated abrasive articles having abrasive grains arranged in a dot pattern have been made by applying adhesive to a backing in a desired dot pattern. The surface is then flooded with abrasive grains that adhere to the dots of adhesive. This method typically provides multiple abrasive grains at each adhesive position. Alternatively, the adhesive can be continuous and the abrasive grains can be applied in a desired pattern.
Other types of abrasive tools have been made by setting abrasive granules, such as diamonds, into a desired pattern by hand. It does not appear that hand setting of large abrasive granules, such as diamonds, has been employed in a commercially available flexible coated abrasive article.
Abrasive grains, even when tightly graded, vary in size, and are typically of an irregular shape. Some of the problems caused by the irregularly sized and shaped grains have been addressed by using spherical agglomerates of roughly equal size. However, even when tightly graded spherical agglomerates have been used, the inability to regulate the number and position of abrasive grains or agglomerates continues to cause problems, such as uneven cutting rates, and scratches of unacceptable dimensions. These problems are accentuated in microabrasive applications.
U.S. Pat. No. 4,930,266 (Calhoun et al.) discloses an abrasive article able to produce fine finishes at high cutting rates. Calhoun et al. disclose a printing process to position individual abrasive grains or agglomerates in a regular, predetermined pattern. Thus, the article described in Calhoun et al. provides an abrasive article that is able to produce a relatively predictable, consistent, and repeatable finish.
However, there remains a need for an abrasive article that can provide a predictable, consistent, repeatable finish to a surface. There is also a need for an abrasive article in which abraded material can be easily removed from the surface of the abrasive article.